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From: Mark Rutland <mark.rutland@arm.com>
To: Arnd Bergmann <arnd@kernel.org>
Cc: Misono Tomohiro <misono.tomohiro@jp.fujitsu.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	SoC Team <soc@kernel.org>, Olof Johansson <olof@lixom.net>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Arnd Bergmann <arnd@arndb.de>
Subject: Re: [RFC PATCH 00/10] Add Fujitsu A64FX soc entry/hardware barrier driver
Date: Fri, 8 Jan 2021 15:51:10 +0000	[thread overview]
Message-ID: <20210108155110.GC84941@C02TD0UTHF1T.local> (raw)
In-Reply-To: <CAK8P3a34aPUwjAXoh20E-PT6vG6gbW_itAXVQAYrhsHZbzqRsQ@mail.gmail.com>

On Fri, Jan 08, 2021 at 03:23:23PM +0100, Arnd Bergmann wrote:
> On Fri, Jan 8, 2021 at 1:54 PM Mark Rutland <mark.rutland@arm.com> wrote:
> > As a general rule, we avoid the use of IMPLEMENTATION DEFINED features
> > in Linux, as they pose a number of correctness/safety challenges and
> > come with a potentially significan long term maintenance burden that is
> > generally not justified by the features themselves. For example, such
> > features are not usable under virtualization (where a hypervisor may set
> > HCR_EL2.TIDCP, or fail to context-switch state that it is unaware of).
> 
> I am somewhat less concerned about the feature being implementation
> defined than I am about adding a custom user interface for one
> platform.

I completely agree that adding a custom interface that's platform
specific is undesireable.

> In the end, anything outside of the CPU core that ends up in a SoC
> is implementation defined, and this is usually not a problem as long
> as we have an abstraction in the kernel that hides the details from
> the user, and the system is still functional if the implementation is
> turned off for whatever reason.

I think that peripherals and other bits out in the SoC are quite
different to things built into the CPU, where there's inevitably most
significant and subtle interactions with the architecture, and can be so
closely coupled as to not have a good point to apply abstraction. We
have common ways of abstracting storage devices, but the same is not as
true for userspace instructions.

Thanks,
Mark.

WARNING: multiple messages have this Message-ID (diff)
From: Mark Rutland <mark.rutland@arm.com>
To: Arnd Bergmann <arnd@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Misono Tomohiro <misono.tomohiro@jp.fujitsu.com>,
	SoC Team <soc@kernel.org>, Olof Johansson <olof@lixom.net>,
	Will Deacon <will@kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC PATCH 00/10] Add Fujitsu A64FX soc entry/hardware barrier driver
Date: Fri, 8 Jan 2021 15:51:10 +0000	[thread overview]
Message-ID: <20210108155110.GC84941@C02TD0UTHF1T.local> (raw)
Message-ID: <20210108155110.alH64ShFmD4-q_VP5Hgw2ulQ1dh4Y1l3HZ5ASQ4QQdY@z> (raw)
In-Reply-To: <CAK8P3a34aPUwjAXoh20E-PT6vG6gbW_itAXVQAYrhsHZbzqRsQ@mail.gmail.com>

On Fri, Jan 08, 2021 at 03:23:23PM +0100, Arnd Bergmann wrote:
> On Fri, Jan 8, 2021 at 1:54 PM Mark Rutland <mark.rutland@arm.com> wrote:
> > As a general rule, we avoid the use of IMPLEMENTATION DEFINED features
> > in Linux, as they pose a number of correctness/safety challenges and
> > come with a potentially significan long term maintenance burden that is
> > generally not justified by the features themselves. For example, such
> > features are not usable under virtualization (where a hypervisor may set
> > HCR_EL2.TIDCP, or fail to context-switch state that it is unaware of).
> 
> I am somewhat less concerned about the feature being implementation
> defined than I am about adding a custom user interface for one
> platform.

I completely agree that adding a custom interface that's platform
specific is undesireable.

> In the end, anything outside of the CPU core that ends up in a SoC
> is implementation defined, and this is usually not a problem as long
> as we have an abstraction in the kernel that hides the details from
> the user, and the system is still functional if the implementation is
> turned off for whatever reason.

I think that peripherals and other bits out in the SoC are quite
different to things built into the CPU, where there's inevitably most
significant and subtle interactions with the architecture, and can be so
closely coupled as to not have a good point to apply abstraction. We
have common ways of abstracting storage devices, but the same is not as
true for userspace instructions.

Thanks,
Mark.

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linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2021-01-08 15:51 UTC|newest]

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-08 10:52 [RFC PATCH 00/10] Add Fujitsu A64FX soc entry/hardware barrier driver Misono Tomohiro
2021-01-08 10:52 ` Misono Tomohiro
2021-01-08 10:52 ` [PATCH 01/10] soc: fujitsu: hwb: Add hardware barrier driver init/exit code Misono Tomohiro
2021-01-08 10:52   ` Misono Tomohiro
2021-01-08 10:52 ` [PATCH 02/10] soc: fujtisu: hwb: Add open operation Misono Tomohiro
2021-01-08 10:52   ` Misono Tomohiro
2021-01-08 10:52 ` [PATCH 03/10] soc: fujitsu: hwb: Add IOC_BB_ALLOC ioctl Misono Tomohiro
2021-01-08 10:52   ` Misono Tomohiro
2021-01-08 13:22   ` Arnd Bergmann
2021-01-08 13:22     ` Arnd Bergmann
2021-01-12 11:02     ` misono.tomohiro
2021-01-12 11:02       ` misono.tomohiro
2021-01-12 12:34       ` Arnd Bergmann
2021-01-12 12:34         ` Arnd Bergmann
2021-01-08 10:52 ` [PATCH 04/10] soc: fujitsu: hwb: Add IOC_BW_ASSIGN ioctl Misono Tomohiro
2021-01-08 10:52   ` Misono Tomohiro
2021-01-08 10:52 ` [PATCH 05/10] soc: fujitsu: hwb: Add IOC_BW_UNASSIGN ioctl Misono Tomohiro
2021-01-08 10:52   ` Misono Tomohiro
2021-01-08 10:52 ` [PATCH 06/10] soc: fujitsu: hwb: Add IOC_BB_FREE ioctl Misono Tomohiro
2021-01-08 10:52   ` Misono Tomohiro
2021-01-08 10:52 ` [PATCH 07/10] soc: fujitsu: hwb: Add IOC_GET_PE_INFO ioctl Misono Tomohiro
2021-01-08 10:52   ` Misono Tomohiro
2021-01-08 10:52 ` [PATCH 08/10] soc: fujitsu: hwb: Add release operation Misono Tomohiro
2021-01-08 10:52   ` Misono Tomohiro
2021-01-08 13:25   ` Arnd Bergmann
2021-01-08 13:25     ` Arnd Bergmann
2021-01-12 10:38     ` misono.tomohiro
2021-01-12 10:38       ` misono.tomohiro
2021-01-08 10:52 ` [PATCH 09/10] soc: fujitsu: hwb: Add sysfs entry Misono Tomohiro
2021-01-08 10:52   ` Misono Tomohiro
2021-01-08 13:27   ` Arnd Bergmann
2021-01-08 13:27     ` Arnd Bergmann
2021-01-12 10:40     ` misono.tomohiro
2021-01-12 10:40       ` misono.tomohiro
2021-01-08 10:52 ` [PATCH 10/10] soc: fujitsu: hwb: Add Kconfig/Makefile to build fujitsu_hwb driver Misono Tomohiro
2021-01-08 10:52   ` Misono Tomohiro
2021-01-08 12:54 ` [RFC PATCH 00/10] Add Fujitsu A64FX soc entry/hardware barrier driver Mark Rutland
2021-01-08 12:54   ` Mark Rutland
2021-01-08 14:23   ` Arnd Bergmann
2021-01-08 14:23     ` Arnd Bergmann
2021-01-08 15:51     ` Mark Rutland [this message]
2021-01-08 15:51       ` Mark Rutland
2021-01-12 10:24     ` misono.tomohiro
2021-01-12 10:24       ` misono.tomohiro
2021-01-12 14:22       ` Arnd Bergmann
2021-01-12 14:22         ` Arnd Bergmann
2021-01-15 11:10         ` misono.tomohiro
2021-01-15 11:10           ` misono.tomohiro
2021-01-15 12:24           ` Arnd Bergmann
2021-01-15 12:24             ` Arnd Bergmann
2021-01-19  5:30             ` misono.tomohiro
2021-01-19  5:30               ` misono.tomohiro
2021-02-18  9:49             ` misono.tomohiro
2021-02-18  9:49               ` misono.tomohiro
2021-03-01  7:53               ` misono.tomohiro
2021-03-01  7:53                 ` misono.tomohiro
2021-03-02 11:06               ` Arnd Bergmann
2021-03-02 11:06                 ` Arnd Bergmann
2021-03-03 11:20                 ` misono.tomohiro
2021-03-03 11:20                   ` misono.tomohiro
2021-03-03 13:33                   ` Arnd Bergmann
2021-03-03 13:33                     ` Arnd Bergmann
2021-03-04  7:03                     ` misono.tomohiro
2021-03-04  7:03                       ` misono.tomohiro
2021-01-12 10:32   ` misono.tomohiro
2021-01-12 10:32     ` misono.tomohiro

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